Solar radiation has long been recognized as an energy source with many potential applications. However, until recently the ease of recovery and relatively low cost of fossil fuels have resulted in the postponement of efforts to utilize this virtually limitless and non-polluting energy source. Present concern over the depletion of fossil fuels has now brought about renewed interest in tapping the energy inherent in the sun's radiation.
Flat-plate solar collectors are commonly used for hot water and space heating. However, flat-plate collectors possess certain inherent disadvantages which deter wider application. Specifically, flat-plate collectors lose efficiency as the collector temperature increases over the temperature of the ambient atmosphere. Since the entire upper surface area of the collector is available for transferring heat to the outside, heat loss increases as the temperature of the collector rises. Not only does this heat loss problem reduce the collector's efficiency, it also imposes a practical limit on the temperature to which a fluid interfacing the collector can be raised. Hence, flat-plate collectors have only been used for relatively low temperature heat applications, such as space heating, and have not been suitable for higher temperature fluid applications, such as absorption cooling and other thermodynamic cycles. An additional disadvantage associated with flat-plate collectors is the cost of the relatively large surface area of materials required to absorb incident light.
In order to attain higher temperatures than possible with flat-plate collectors, concentrating collectors have been developed. Such devices concentrate incident solar radiation upon a relatively small absorption area, typically by some type of imaging process. Although higher temperatures have been obtained with such concentrating collectors, they too have certain deficiencies. In particular, in order to capture solar radiation they must at least roughly track the path of the sun. This requires a complicated mechanism for moving the concentrating collector which adds a substantial expense to the overall device and involves regular maintenance and the possibility of mechanical failure. Furthermore, because these concentrating collectors are designed for capturing direct sunlight, much of the diffuse sunlight goes uncollected. As a result, on overcast days, and in northern latitudes where a large percentage of incident sunlight is diffuse, such collectors are not optimally functional.
One solution to the problems inherent with both flat-plate and concentrating collectors is to passively concentrate incident sunlight, both direct and diffuse, without the aid of a tracking mechanism. Several of these non-tracking solar concentrating collectors exist in the prior art, such as those of U.S. Pat. Nos. 3,915,148; 3,923,381; 3,964,464 and 3,780,722. However, unlike the invention disclosed herein, none of these devices collimate the sun's rays which they collect. Such collimation permits improved concentration upon an absorbing target by a simple and relatively inexpensive collector possessing a number of novel and advantageous features as revealed in the following disclosure.
The principal object of this invention is to provide a new and useful device for collecting both direct and indirect sunlight and for concentrating solar energey in amounts sufficient for heating and/or cooling buildings.
It is another object of the invention to provide an improved solar energy collector having a new and useful system of curved, laminated transparent elements for collimating solar radiation and concentrating solar energy by directing collimated radiation upon an absorbing target.
It is a further object of the invention to provide an improved device for concentrating solar energy which does not require an expensive and complicated tracking mechanism.